This invention generally relates to electrochemical cells that utilize an electrode having an electrochemically active material in particulate form. More specifically, this invention pertains to electrochemical cells having a quantity of agglomerated zinc particles in the anode.
Cylindrically shaped electrochemical cells are suitable for use by consumers in a wide variety of devices such as flashlights, radios and cameras. Batteries used in these devices typically employ a cylindrical metal container to house two electrodes, a separator, a quantity of electrolyte and a closure assembly that includes a current collector. Typical electrode materials include manganese dioxide as the cathode and zinc as the anode. An aqueous solution of potassium hydroxide is a common electrolyte. A separator, conventionally formed from one or more strips of paper, is positioned between the electrodes. The electrolyte is readily absorbed by the separator and anode.
Commercially available cylindrical alkaline batteries use an anode that includes zinc in particulate form. The anode is a gel that has absorbed an aqueous electrolyte. The zinc particles are uniformly dispersed within the gel so that particle-to-particle contact establishes an electrically conductive matrix throughout the anode. A current collector contacts the zinc and provides an electrically conductive path between the anode and one of the cell's terminals.
Due to the ever present desire to provide consumers with better performing batteries, battery engineers are constantly striving to improve the length of time that a battery will power a consumer's device. One key objective is to improve the service of the battery on high drain. For example, JP Kokai 57[1982]-182972 discloses that the high discharge characteristic of a battery can be improved by incorporating 5-30 weight percent of the zinc as particles with a particle size of 25 μm or smaller. Unfortunately, there are problems associated with increasing the quantity of zinc dust or fines. One disadvantage is that an increase in the percentage of zinc dust and/or zinc fines results in increased gassing within the cell. Another disadvantage is that the increase in the quantity of zinc dust causes a corresponding increase in the viscosity of the anode gel which results in processing problems in high speed manufacturing processes.
An alternative to adding zinc dust or fines to an anode gel is to decrease the average diameter of the zinc particles whereby the total surface area of the zinc increases proportionally. Unfortunately, as the average diameter of the zinc particles decreases, there is a corresponding increase in the percentage of zinc fines or dust. One disadvantage to increasing the quantity of zinc dust by decreasing the average particle size is that the dust may become separated from the larger zinc particles during transit and storage of the zinc prior to its incorporation into an anode gel. The zinc dust particles also tend to become separated from the larger zinc particles during the manufacture and transit of the anode gel. Unintended separation of the large particles from the small particles can negatively impact the quality of the anode gel and the quality of the cell containing the anode gel. Consequently, although battery manufacturers would like to improve the battery's service by including greater quantities of zinc dust or fines in the anode formulation, the above described problems limit the quantity of zinc dust that can be incorporated into the anode formula.
Therefore, there exists a need for a process that enables battery manufacturers to incorporate greater quantities of zinc dust in the anode formulation without sacrificing efficiency in the cell manufacturing process. There also exists a need for an electrochemical cell that incorporates zinc dust into the anode in a manner that effectively prevents the zinc dust from becoming separated from the larger zinc particles during cell manufacturing and/or when the cell is used by the consumer.